DESCRIPTION: CD8+ T-cells control immune responses, and recent studies suggest that this regulation is, in part, specifically directed towards T-cell receptor (TCR) structures expressed by CD4+ cells. To further study the function of CD8+ T-cells in immune regulation, the investigators studied the role of CD8+ T-cells in regulating superantigen induced CD4+ T-cell responses. They determined that the delayed deletion of CD4+Vbeta8+ T-cells following SEB injection is prevented by treatment of animals with anti-CD8 antibody and is not observed in beta2 M-/-mice. CD8+ T-cells obtained from SEB treated animals and stimulated in vitro with CD4+Vbeta8+ cells preferentially kill activated CD4+Vbeta8+ but not CD4+Vbeta-T-cells. CD8 anti-Vbeta cytotoxicity is dependent on beta2 microglobulin and is inhibited by antisera to Qa-1 but not by antibody to MHC class I-a. Furthermore, in recent studies, the investigators show that CD8 anti-Vbeta8 T-cells kill T hybridomas transfected with Vbeta8 cDNAs but not other VbetacDNAs. These data demonstrate that immunoregulatory CD8+ T-cells recongnize TCR Vbeta determinants and Qa-1 molecules expressed on antigen activated CD4+ T-cells. The investigators envision that Vbeta specific CD8+ T-cells of this type may regulate immune responses by direct interaction with antigen activated CD4+ cells. In this application, they will extend their analysis of CD8 anti-Vbeta T-cells in ways designed to further elucidate their normal biology and their potential role in autoimmunity and superantigen-mediated diseases. In Aim 1, they will investigate the ability of CD8 anti-Vbeta T-cells to regulate CD4+ T-cells in mice with defective Fas and FasL molecules and will examine the ability of normal or FasL mutant CD8 anti- Vbeta T-cells to kill CD4+ T-cells from normal or Fas-mutant mice. Furthermore, in adoptive transfer experiments, they will determine if wild-type CD8+ cells correct the defective SEB-induced deletion of Vbeta cells in FasLgld mice. In Aim 2, they will identify specific Vbeta and Jbeta sequences used by CD8 anti-Vbeta T cells and the length of these TCRbeta CDR3 regions and use this information to follow the development of CD8 anti-Vbeta8 T cells in vivo both in superantigen induced responses and during EAE. In Aim 3, the invesitgators will determine if CD8 anti-Vbeta T-cells differentially regulate the emergence of TH1 and TH2 cells following exposure to SEB and if CD8 anti-Vbeta T cells differ in their ability to be induced by or to kill TH1 versus TH2 cells. Moreover, based on observations that EAE is mediated by TH1 cells and that clinical EAE is moderated by CD8 T-cells, they will determine if CD8 T-cells regulate TH subset differentiation in EAE.